1. Field of the Invention
The present invention relates to a control device for an internal combustion engine.
2. Description of the Related Art
Japanese Unexamined Utility Model Publication No. 3-119551 discloses a control device for a fuel injection system with an injector for injecting fuel directly into the cylinder of an internal combustion engine. This disclosure explains that the fuel injector easily leaks fuel into a cylinder when fuel is not to be injected, i.e., when fuel cut is carried out, because the pressure of fuel in a pressure chamber of the fuel injection system is kept high. To prevent the fuel leak, the control device lowers the fuel pressure in the pressure chamber during a fuel cut. The control device then corrects a fuel injection period directly after the fuel injection is restarted because a fuel pump in the fuel injection system can not quickly increase the lowered fuel pressure to a required level.
A fuel leak from a fuel injector is caused due to the inaccurate processing of the seat part of the fuel injector, the wear thereof for a long time of use, or the inclusion of a foreign object therein. In all cases, if the fuel leak per unit time is large enough to hinder the operation of the engine, the fuel injector must be replaced. On the other hand, when the fuel leak does not require replacement of the fuel injector, the above-mentioned control device tends to prevent a fuel leak during a fuel cut by lowering the pressure of fuel in the pressure chamber. However, if the fuel injector is designed to improve the sealing of the fuel injection hole by the use of the high fuel pressure in the pressure chamber, the leak will be worsened due to a decrease in the fuel pressure. In such fuel injector, even if the engine is stopped and the fuel pump is stopped and thus the fuel pressure in the pressure chamber becomes equal to an atmospheric pressure, a fuel leak occurs. Accordingly, the above-mentioned control device is incapable of preventing this kind of a fuel leak.
If the fuel leakage per unit time is small, it will not hinder the operation of the engine. However, once the fuel leakage rises to a certain level during stoppage of the engine, a large part thereof will be unburned and emitted outside when the engine is restarted, to provide a poor-quality emission.